Modeling and analysis of the compliance and stability of enveloping grasps

We address the stability and performance of enveloping grasps. An enveloping grasp is defined in which robot fingers or arms grasp an object by making contact at points other than just the fingertips or end-effectors. Previous work has demonstrated that enveloping grasps are more robust. However their analysis is difficult because they are usually statically indeterminate and overconstrained. In this paper we develop a method for modeling the stiffness of a grasp. It is based on a model of compliance at each contact and a model of the joint compliance at each joint. It incorporates the kinematics of three-dimensional contact in addition to the kinematics of the robot arm/finger. In particular the methodology is used to show that force closure does not necessarily imply stability.